1. Field of the Invention
The present invention relates to an automobile lamp used as a headlight, a stop lamp, a turn-signal lamp, a back-up lamp, or the like, and more particularly to a composition of the automobile lamp having an outer lens without any prismatic cuts for diffusion or diffraction of reflected light. Light distribution patterns are formed and controlled mainly by a reflector.
2. Discussion of the Related Art
FIGS. 8 and 9 illustrate a conventional automobile lamp 90 comprising a light source 92, a reflector 91 having an aperture, a shade 94 covering the light source 92, and an outer lens 93 covering the aperture of the reflector 91. The reflector 91 has a free-form surface or a complex surface, which is a substantially single smooth curved surface that is not determined by a quadratic curved line, such as a rotated parabolic surface, a parabolic cylinder, a hyperboloid, or a plane. The reflector 91, having a free-form or complex surface, is able to form light distribution patterns itself by controlling reflecting directions of light rays when the light rays emitted from the light source 92 are reflected by the reflector 91. Therefore, no prismatic cut is required for the formation of the light distribution patterns, and the inside composition of the automobile lamp 90, such as the reflector 91, the light source 92, and the shade 94 can be seen from outside through the outer lens 93.
The conventional automobile headlight 90 has the following problems. First, since light that is reflected on the rearmost portion of the reflector 91 is prohibited by an inner side surface of the aperture or an extension of the reflector 91, it is difficult to obtain sufficiently wide light distribution patterns in a horizontal direction. Second, on formation of light distribution patterns by the reflector 91, the reflector 91 is divided into different portions, such as a first reflecting surface for illuminating center front, a second reflecting surface for illuminating left front, and a third reflecting surface for illuminating right front. Reflected light from respective reflecting surfaces combine to form a light distribution pattern. However, since the contour of respective reflecting surfaces are rather conspicuous, the light distribution pattern, comprising light from each reflecting surface, does not seem to have a uniform luminous flux density distribution. The pattern is instead easily perceived as a combination of different reflecting portions having different luminous flux density because of luminous density gaps between the different reflecting portions. Third, since the inside composition of the outer lens 93 can be seen through the outer lens 93, headlight parts that detract from the headlight's aesthetic appearance, such as the base of the light source 92 or the shade 94, can be seen when looking into the headlight 90 from outside in every direction, except when looking through the center front. As a method to prevent the shade 94 and the base from being seen from outside, the outer lens 93 has prismatic cuts 93a around a portion corresponding to the shade 94, as depicted in FIG. 9. However, the base of the light source 92 can still be seen when looking into the headlight 90 at an angle from the outside. Additionally, the prismatic cuts 93a decrease the uniformity of luminous flux density distribution, since light reflected by the reflector 91, which has already been sufficiently diffused, is further diffused when the light passes through the prismatic cuts 93a.